Main outcomes of the evolution by natural selection: adaptation, extinction, coevolution and speciation.

Key Information

The Birth of the Theory of Evolution

Before Darwin the general consensus was that species were created independently by some extranatural force, and that they died out without any major change. So, which were the steps needed for a theory of evolution of the biological species to be accepted in the XIX century?

Accepting the idea that species can change during their life span.

Accepting the idea that species can change so much that they can even generate new species, either by diversification (cladogenesis) or by a global transformation of one whole species (anagenesis).

Accepting the idea (that looks like an inevitable result of the previous one) of a common descent, i. e., that all species are related, have a kinship, and they all come from a common ancestor.

Accepting the idea that the Earth is old enough for these huge changes to have enough time to occur... so slowly that can't even be perceived during a human life span.

And most notably: knowing of any acceptable mechanism by which these types of changes can occur.

Considering that not so long ago, the Anglican bishop James Ussher had stated that the Earth had been created the night preceding 23 October 4004 BC, the idea of an old Earth was, quite possibly, the necessary precondition for all the others to be even borne in mind by anyone. And this revolutionary idea was just there in the right moment, when Darwin started his five years long journey in the Beagle, and was given the first volume of Charles Lyell's Principles of Geology, which set out the idea of masses of land slowly rising or falling over immense periods of time to finally yield the geological features that can be observed in present time. According to Lyell, the Earth was much older than what was thought by that time, probably even millions of years old (some 4,560 years old, to be more precise, and as we know today).

The concept of a gradual change of biological species, now that Darwin knew that there was enough time for it, arose from the observation of different races of tortoises, finches and others, adapted to the particular environments that the Galápagos islands had to offer. And more particularly, to the different nutritional niches available; while some finches had a beak specialised in cracking hard nuts, others were the perfect weapon for chasing insects, etc. And considering that those islands are some 1,200 km away from the continent, it was clear to Darwin that all those finches (or tortoises) had had to come from one (or a few) small group of ancestors that, departing from the mainland, happened to make their way to the islands. The Galápagos finches had evolved on-site, as it was highly unlikely that all those varieties could have possibly reached the islands from the continent, one by one.

That panorama was clearly speaking about gradual transmutation of those animals by adaptation to different environments (species can change), and with it, Darwin's mechanism of evolutionary change had started to develop.

But was that slow and gradual change powerful enough to produce new species, or were all those differently adapted finches simple varieties of the same species? Friends are to come to the rescue when needed, and so it was with Darwin's mate John Gould, an ornithologist, who announced that the specimens of finches that Darwin brought back to England after his trip belonged, in fact, to three different species. In Darwin's mind, that meant that gradual adaptation to the environment can actually produce new species.

Finally, how do species get to adapt to each one of the many specific environments that Nature provides? How can a population gradually reach its ecological niche, one that allows it to survive and thrive for generations? That was the last and greatest obstacle to overcome, and recent History showed that clearly. Jean-Baptiste de Lamarck had already come up with similar thoughts to Darwin's a couple of decades before the Beagle departed: species evolve, and do it by gradual adaptation to their environment. But Lamarck could never demonstrate that acquired-on-life traits can be passed on to the offspring, and we know nowadays that that just can't happen: the genes of your eggs or sperms will not change because of you dying your hair. And this is how Lamarck passed to History as an unsuccessful attempt to explain the how and the why of the evolutionary process.

But not Darwin. It turns out that among the many different types of individuals that are randomly produced every generation in every species, some happen to be better suited to their environment than others: the former feed better, grow faster, survive longer and as a result... reproduce more than the latter. And as the traits that make them the fittest were inherited, they will also pass those traits to their children. As a final result, those traits will be more present in the next generation than those that conferred a lesser success. This was what Darwin (and Alfred R. Wallace) elucidated, and that's why everyone is now celebrating his 200th anniversary. Or almost everyone.

Main Evolutionary Ideas in Linné, Lamarck and Darwin

Linné

Lamarck

Darwin

1

Species can change gradually over their lifetime.

N

Y

Y

2

Species change by means of a progressive improvement in their adaptation to the environment.

n/a

Y

Y

3

Species can change so much that each one of them can transmute into a new different species (anagenesis).

n/a

Y

Y

4

Species can also change in a way that one species can give birth to several new descendent species by branching off (cladogenesis).

n/a

N

Y

5

All species are thus related and come from a common ancestor.

n/a

N

Y

6

Evolutionary change by progressive adaptation to the environment happens because every living being has an innate tendency to improve its adaptation to the environment, and so organs are developed or atrophied during life as needed.

n/a

Y

N

7

Acquired-on-life changes (such as the atrophy or development of organs) are inherited.

n/a

Y

N

8

Evolutionary change by progressive adaptation to the environment happens because the fittest leave a greater offspring.

n/a

N

Y

9

The traits that confer a greater fitness were inherited from the parents, and so they can be passed on to the children.

n/a

N

Y

N.B.: 4 and 5 go together as 5 is the result of 4; 6 and 7 go together and make Lamarck's idea of the mechanism of evolutionary change; 8 and 9 go together and make Darwin's idea of the mechanism of evolutionary change.

N.B.: Carl von Linné (= Carl Linnaeus) is best known for having developed the binomial (= binominal) nomenclature of the species, by which all species have an official scientific name, called binary name or binomen because it is made of two latinised words. Thus the "wolf" is called "lobo" in Spanish or "loup" in French, but may be also called "Canis lupus" all throughout the world. The binomen is made of the genus name ("Canis") and an specific name ("lupus").

How Does Natural Selection Work?

Natural Selection is all about a central event: some individuals reproduce more than others. And this has a cause and a result. Step by step:

There are many different types of individuals in any biological population. We all can see that. And it is due to mutation and recombination. Mutation increases the number of possible alleles for every loci throughout time, and even creates new loci, or gets rid of loci or alleles. But in the long run mutation tends to increase the number of genes (either alleles or loci) for every species. Mutation takes place mostly due to errors during the duplication of DNA prior to cell division. Also, the recombination of loci during meiosis multiplies the number of different possible gametes that any individual can produce.

Different types of individuals interact differently with their environment. Some of them are stronger, faster, bigger, smarter... and so some of them grow faster and reach fertility sooner, hide better from predators and manage to sort the threats out better, are more efficient absorbing nutrients or chasing the prey, are more convincing when looking for someone of the opposite sex to mate...

The individuals that have more successful interactions with their environment leave a greater offspring. No way it can be otherwise. If you reach fertility faster, survive longer, and your nutritional efficiency leaves you more free time, chances are that you are going to have a greater reproductive success.

Many of the traits that make these individuals more successful are inherited. Although in some species (us!) some "rules for success in Life" can be learned, capability for learning is itself an inherited trait. And, although your genes don't determine the weight that you'll have when you are 25, they do determine a certain range or weights you are likely to fall within.

The alleles of the individuals with a greater reproductive success will be present with a higher frequency in the next generation, and vice versa. As a result, the phenotypic traits coded by the successful alleles will be more present in the next generation, and this noticeable phenotypic change improves the overall fitness of the population gradually, generation after generation.

In short, Natural Selection takes place through the following sequence of events:

Variation due to mutation and recombination.

Differential fitness.

Differential reproduction.

Heritability of phenotypic traits.

Change in the frequencies of the alleles of a population.

Overall phenotypic change in a population.

The Formation of New Species

The formation of new species or speciation is one of the main outcomes of the evolution of Life, the opposite to extinction, and the most visible result of adaptation.

Sexually reproducing species (virtually all that exist, except prokaryotes) are defined as those groups of individuals that can leave fertile offspring by sexual reproduction, and thus share a common gene pool: the genome of species. This is so because sexual reproduction can be considered as a way to produce new combinations of genes (new genotypes) by means of sharing half of the genes of each one of the two partners. Sexual reproduction is a bit like dealing sets of, say, five cards after having shuffled the deck. In the analogy, each card would be a gene, each set of five cards the genotype of a new individual, and the deck of cards is the genome of the species.

The members of the same species also share the same ecological niche, this is, they dwell on the same habitat, they feed the same way, they prefer a similar amount of humidity or sunlight, the are prey to the same predators, etc.

If two individuals of opposite sex that can leave fertile offspring by sexual reproduction belong to the same species, then, speciation must be the process by which two populations, that originally belonged to the same species, split apart and, after a time of adaptation to different environments (or ecological niches), evolve differently to the end that eventually they become unable to leave fertile offspring by sexual reproduction. This end point of speciation is called reproductive isolation.

This process can take place by different ways. Sometimes the appearance a new geographical barrier is the decisive event. That is the case of the Galápagos tortoises, presumably descendants of a common ancestor, that after colonising the different islands of the archipelago, the sea between the islands posed an almost invincible obstacle for them to meet and mate. This way, the different populations settled down in the different islands, couldn't share a common gene pool anymore, and natural selection made them to evolve differently by improving their adaptation to each particular island. Eventually, they changed so much that if individuals of these different populations happened to meet due to the sea currents or the action of men, they were so different that they would not able to leave fertile offspring by sexual reproduction. Those different populations were now different species.

But speciation does not always need huge geographic barriers. In the case of Galápagos finches, different species appeared in the same islands because when this virgin territory was colonised by their ancestors, a variety of ecological niches were at their disposal, and while some of the finches specialised in feeding off insects, other preferred grains, and so forth. They shared a common habitat, but occupied different places in it and performed different ecological roles. The enhancement of that specialisation (the improvement of their adaptation) to each specific ecological niche by means of natural selection did the rest, and, like the tortoises, with time enough took them to be so different that one day they were reproductively isolated.

But how different two individuals of the opposite sex have to be, to be reproductively isolated? The answer is: either...

So different that the male wouldn't be able to fertilise the female, because...

They don't attract each other sexually anymore: courting does not work for them;

Their genitals have become incompatible;

The sperms are unable to make their way towards the egg, in the case of mammals;

etc.

Or so different that even if the male can fertilise the female, they can't leave fertile offspring, because...

The zygote can't divide by mitosis (consider a sperm with 23 chromosomes and an egg with 24: this makes a total diploid number of 47, which is odd, and mitosis cannot take place with an odd number of chromosomes);

Understanding Evolution.An even better and wider collection of articles to tell you everything you ever wanted to know about Evolution and never dared to ask. The Evolution 101 course is just the perfect introduction to the topic, nicely complemented with good quality images.

Movies and Animations

The Birth of the Theory of Evolution

On the origin of species: first paragraphs

Listen to the starter paragraphs of the most influential book in the History of Science, Darwin's "On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life".

Evolution primer: who was Charles Darwin?

Discover how Darwin's curiosity, his passion for natural history, his voyage on the Beagle, and his use of the scientific process led to the publication of his groundbreaking book.

Well explained overview of the process of natural selection and how old Darwin's theory itself has had to adapt to survive under the new discoveries of Genetics.

The Theory of Evolution made easy

Learn some evidence that makes evolution an accepted fact among biologists all over the world.

Evolution primer: how do we know evolution happens?

Learn about evolution through the fossil remains of whales' land-dwelling ancestors

Evolution primer: how does evolution really work?

Travel to Ecuador to see how the process of natural selection operates in populations of rainforest hummingbirds.

Evolution primer: why does Evolution matter now?

Learn how tuberculosis is transmitted and why the evolution of multi-drug resistant strains of TB in Russia affects us all.

Gradual evolution

The odds that such a complex organ as the human eye could have showed up all at once, and just randomly, are extremely low, creationists say. But the chances for it to appear gradually, step by step, are really high, as this video explains.

Gradual evolution of a complex organ: the eye

But can something like the human eye, that seems to only have any sense once it was fully developed, really appear by gradual evolution? Richard Dawkins explains how.

Science and Faith / Evolutionism and Creationism

Evolution primer: isn't Evolution just a theory?

Learn the difference between the scientific and everyday use of key vocabulary words.

Evolution primer: why is Evolution controversial anyway?

Consider different points of view, as scientists, religious leaders, and college students share their opinions about evolution, science, and religious faith.

Creation science made easy

Learn why creation science is not science, and why the creation theory is not even a theory.

Audios

The Birth of the Theory of Evolution

Naked evolutionIt's 150 years since Darwin's theory of Evolution was presented to the Linnean Society, and so we've Naturally Selected the Science of Evolution! We find out why scientists have revisited a textbook example of natural selection in action, find out why horny sheep are gambling on good weather and how bacteria in the lab can evolve into a new species! We find out why tragedy almost kept Darwin's ideas from ever being seen, by looking at the archives of his own letters. Plus, why crocodiles chat from inside their eggs, a new way to send messages underwater and why Martian soil would be good for growing cabbages! And in kitchen science we find out which surface is best for keeping ice cool.Streamed from the Naked Scientists podcast

Lamarck's evolutionBefore Darwin, Jean-Baptiste de Lamarck devised the first theory of evolution in 1809. However, it was discredited by most in the scientific community once Darwin published his theory of evolution by natural selection, 50 years later. Ross Honeywill tells us this fascinating story.Streamed from the Ockham's Razor podcast

Science Helpdesk is a website meant to help on developing the scientific contents of the Bilingual Project Integrated Curriculum designed by the Spanish Ministerio de Educación y Ciencia and the British Council.

Science Helpdesk is designed, developed and published by Arturo J. Murias, currently working in the I.E.S. Arribes de Sayago (Bermillo de Sayago, Zamora, Spain) as a Science teacher in Secondary Education.

This website is under continuous development carried about by one single person. This means that you might notice eventual defects in its rendering or its working—please use the "Contact" form to report to the webmaster, and that its contents and features are still subject to further completion.

This website is regularly tested in the latest versions of Chrome, Firefox and Opera, all of them in Windows. Testing for other browsers and old versions of the latter is rarely done, and using them might result in unexpected display or behaviour defects. Specifically, you are advised to not to use versions 8 or older of Internet Explorer.

Parts of this site (specifically photos and videos) are used without permission, but within fair use, for the purposes of education. Copyright of those contents belong to their authors, mentioned where known. The contents created by the author of this website can be freely distributed under the terms of a Creative Commons License.

The following form is provided for you to help on the development of this website by sending your suggestions or reporting eventual problems when browsing the site. The message will be sent to the webmaster's mailbox who, eventually, will give you a reply.All fields are mandatory.

Your name:

Your e-mail:

Your message:

Use this form to tell your friends to come and visit Science Helpdesk.All fields are mandatory.